An image sensor is a semiconductor device for converting an optical image into an electric signal. The image sensor may be generally classified into a charge coupled device (CCD) image sensor and a complementary metal oxide silicon (CMOS) image sensor (CIS).
A CIS may include a photodiode and a MOS transistor formed in a unit pixel, and generally obtains an image by sequentially detecting electrical signals of unit pixels in a switching manner.
In a related art CIS structure, the photodiode and the transistor are horizontally arranged.
Although the related art horizontal-type CIS has addressed some of the limitations of CCD image sensors, a conventional horizontal-type CIS image sensor still has several problems.
For example, in a conventional horizontal-type CIS, a photodiode and a transistor are horizontally formed adjacent to each other on a substrate. Therefore, an additional region for forming the photodiode is required, which may decrease the fill factor and limit the possibility of resolution.
Also, in the conventional horizontal-type CIS, it is very difficult to optimize processing by concurrently forming the photodiode and the transistor.